1. Field of the invention
The invention relates to a power supply switchover device for electrical apparatus that associates a storage battery and another source of electrical power which the storage battery is adapted to temporarily replace or interface, as well as to teleaction terminal equipment fitted with a power supply switchover device of this type.
Many items of electrical apparatus are provided with an auxiliary or main power supply operating on the basis of a storage cell or battery, frequently incorporated into the apparatus, which is designed to be recharged from an external source of electrical energy.
In this category, we find electrical apparatus the power supply of which, normally provided from an external source of electrical power such as the commercial AC supply, is temporarily provided by means of a storage battery should there be a failure or dropout of the normal external power source.
Also in this category, we find electrical apparatus, which frequently is portable, and powered by storage batteries that are recharged by connection to a source of energy which is external thereof, when the apparatus is not in use.
In numerous items of apparatus, a power supply switchover device makes it possible to disconnect a storage battery from the apparatus it is powering before the storage battery becomes fully discharged, in order to prevent the apparatus and the storage battery from operating under poor conditions which can lead to faults occurring in the apparatus and to deterioration of the storage battery.
2. Description of the Prior Art
One known solution consists in measuring the voltage at the terminals of the storage battery and in disconnecting the storage battery when this voltage falls to below a predetermined threshold. However, the voltage across the terminals of a storage battery, notably the nickel-cadmium type, tends to rise again when the storage battery is disconnected from the load that it was previously powering.
If no precautions are taken, there is a danger of producing a succession of connections and disconnections of the storage battery about the threshold value chosen for cutout and, as a consequence, there is the possibility of deterioration, and faults appearing.
Moreover, it is important to be able to avoid glitches or very brief breaks in supply when changing from one source to the other, in a manner that is as simple as possible.